There are video coding apparatuses for applying coding processing to frames of an input video in conformity with a certain video coding scheme to generate coded data, i.e., a video bitstream. There are also video decoding apparatuses for receiving such a video bitstream as an input to generate a decoded video.
An example of the video coding schemes is ISO/IEC 14496-10 AVC (Advanced Video Coding). In ISO/IEC 14496-10 AVC, each frame is divided into blocks each having a size of 16×16 pixels, the block being referred to as MB (Macro Block). An MB is further divided into blocks each having a size of 4×4 pixels, the 4×4 pixel block being defined as a minimal unit of coding. An example of block division is shown in FIG. 14, where the spatial resolution of a frame is in a QCIF (Quarter Common Intermediate Format) 4:2:0 format.
The divided blocks are coded based on prediction. Intra-frame prediction predicts an image using a reconstructed image of a current frame of interest for coding processing. Inter-frame prediction, or inter-layer prediction or inter-view prediction, predicts an image using a reconstructed image of a frame coded previous to a current frame of interest for coding processing. Moreover, to reduce compression distortion, in-loop filtering is applied to the reconstructed image of a frame of interest for coding processing. A video coding apparatus and a video decoding apparatus comprise a reference picture memory for storing frames including reconstructed images (reference pictures).
Regarding video decoding apparatuses for decoding a video bitstream output by a video coding apparatus to obtain a decoded video, Patent Documents 1-3, for example, disclose techniques of applying lossy compression to a reference picture in order to reduce the memory bandwidth and/or memory size in the video decoding apparatus, and storing a resulting picture in a reference picture memory.